I've got this strange fin modification in my last breed of bettas. I've got a male and female whose lower fins are attached with their tail fins... is this a new tail mutant or do these already exist. I am attaching a pic of the male here.

rosetails are pretty, but not good for a breeding program ;p am not sure if it does cause spinal deformities but i know it causes scale deformities. pretty fish, and sometimes the anal and caudal fin do fuse together, some fish miss there ventral fins entirely o.o

as for the OP's, Rosetails aren't good for breeding, because the mutation that causes the extra branching can affect the scales, and the health of the betta. and, the added finnage isn't good for them at all.